In recent decades, ultra high pressure intensifiers have been used for a variety of industrial purposes. These intensifiers pressurize water to as high as 30,000 to 60,000 PSI or higher, and the water is often discharged as a high velocity water jet to accomplish such operations as cutting or abraiding material. A common configuration of such an intensifier comprises a piston assembly where there is a larger diameter center piston, and two smaller high pressure pistons extending oppositely from the center piston, with these being enclosed in a suitable cylinder housing. High pressure hydraulic fluid is directed into the larger cylinder containing the center piston to reciprocate the piston assembly back and forth, and the smaller diameter high pressure pistons alternately pump water at very high pressures to one or more orifices (or other output) through which the high pressure water is discharged.
When the piston assembly reaches one end of its stroke, there is a short period of time (e.g. 60 milliseconds) before it starts reversing direction. Then, since water at these very high pressures becomes compressed by as much as fifteen percent, it can take as much as about another 100 milliseconds or so to precompress the water in the cylinder to the operating pressure. Thus, at the end of one stroke of the piston and during the initial compression phase of the stroke, there is a pressure dip in the output. This can be compensated for partially by use of an accumulator.
When two intensifiers are utilized in parallel relationship to deliver high pressure water to the same output, if the intensifiers are operating out of phase, so that one intensifier is on its power stroke while the other one is changing direction, this can help to alleviate the problem of the pressure dips. On the other hand, if the two intensifiers have their piston assemblies reaching the end of a stroke at the same time, the effect of the pressure dip can be rather severe and impair the effective of operation of the system.
Even though two ultra high pressure intensifiers are substantially identical models, under the same operating conditions, each will operate at a slightly different frequency. For example, over a period of time one intensifier may develop a certain amount of leakage around the seals, valves, etc. and this could change its operating frequency. As a practical matter, when the intensifiers are operated to provide a common output, the pressures developed by the two intensifiers should be substantially the same (requiring that the intensifiers would have a common reference pressure by which to operate), and this places certain constraints on the phase control devices that would be practical.